Low frequency relaxation oscillators



Sept. 11, 1956 H. D. KIMP LOW FREQUENCY RELAXATION OSCILLATORS Filed May 27, 1954 F'TE'I. E.

HARRY D. KIMP INVENTOR. BY%W%M HIS ATTORNEY United States Patent Ofiice 2,762,919 Patented Sept. 11, 1956 LOW FREQUENCY RELAXATION O'SCILL'ATORS Harry D. Kimp, San Fernando, 'Calif., assignor to Hoffman Electronics Corporation, a corporation of 'California Application May 27,1954, Serial No. 432,723

4 Claims. (Cl. 250-36) This invention is related to relaxation oscillators and, more particularly, to an improved relaxation oscillator the design of which permits the generation of signal frequencies which are of the order of one cycle per second or less.

In the past, attempts to design apparatus which will generate pulses having a frequency between and /5 cycles per second have been restricted largely to resort to mechanical designs of one form or another, which generally employ an electric motor. Such mechanical designs have proven to be costly to manufacture.

Therefore, it is an object of this invention to provide a low frequency relaxation oscillator which, of itself, possesses means of frequency selection between 5 and /5 cycles per second, for example.

It is a further object of this invention to provide an improved low frequency relaxation oscillator which will lend itself to low-cost manufacture.

According to this invention, a thyratron vacuum tube employs an adjustable grid bias potentiometer, which is a part of the resistance-capacitance circuit having a long time constant, to vary the instant at which thyratron firing will occur. Firing causes a relay to energize to remove anode voltage from the thyratron and discharge the capacitor in the resistance-capacitance circuit. The thyratron ceases to conduct by reason of the removal of anode voltage, the relay becomes de-energized, and the oscillator circuit is restored to its initial condition.

The features of the present invention which are believed to be novel are set forth with particularity in the appended claims. The present invention, both as to its organization and manner of operation, together with further objects and advantages thereof, may best be understood by reference to the following description, taken in connection with the accompanying drawings, in which:

Figure 1 is a schematic diagram of a low frequency relaxation oscillator, according to this invention.

Figure 2 is a graph of the pertinent voltage and current wave forms of the relaxation oscillator shown in Figure 1.

Figure 3 is a schematic diagram showing a practical application of a low frequency relaxation oscillator of Figure 1.

In Figure 1, cathode of thyratron vacuum tube 11 is connected through potentiometer 12 and through resistor 13 to ground. Variable tap 14 of potentiometer 12 is connected to screen grid 15 of thyratron 11. Control grid 16 is connected through resistor 17 to cathode 10. Anode 18 of thyratron 11 is connected to output terminal 19, and also through load resistor 20 to terminal 21 of relay 22. Capacitor 23 is connected between terminals 21 and 24 of relay 22. Terminal 24 of relay 22 is connected to relay arm 25. Cathode 10 of thyratron vacuum tube 11 is connected through resistor 26 and capacitor 27 to relay arm 25. Terminal 28 of resistor 26 is connected to contact 29 of relay 22. Contact 30 of relay 22 is connected to high voltage terminal 31.

2 Output terminal 32 is maintained at ground potential. Negative terminal 33 of the high voltage (B+) supply is connected through switch 34 to ground.

The circuit of Figure 1 operates as follows. Screen grid 15 of thyratron vacuum tube 11 is made the control electrode so that the thyratron firing action will be affected least by operating temperature. Resistor 17 prevents grid 16 from drawing excessive current. Resistor 13 and capacitor 27 may both be of large value and, together with potentiometer 12 and resistor 26, form a resistance-capacitance charging circuit having a long time constant. Capacitor 23 supplies extra energy to keep relay 22 energized over a relatively long period of time and protects relay 22 against transient effects. When switch 34 is closed, current (electron flow) surges through resistor 13, potentiometer 12, and resistor 26 to charge capacitor 27. This current shall be designated as ik, and its wave form is shown in Figure 2 as curve 200. During this charging interval, thyratron 11 is kept out off by reason of the negative bias supplied by potentiometer 12 and applied to grid 15. When this bias voltage falls to the critical value, that is when ik reaches point A in Figure 2, thyratron 11 will fire and thus conduct a large current pulse which will be aided by the discharge in part of capacitor 27. The charging and discharging of capacitor 27 during the time interval just described is represented by curve portions 201 and 202 of curve 203, shown in Figure 2. Anode current and voltage wave forms of thyratron vacuum tube '11 are shown by curves 204 and 205, respectively, of Figure 2. At point B of curve 200 in Figure 2, relay 22 becomes energized, and relay arm leaves contact 30 and touches contact 29. During the time interval when relay 22 is energized (time interval x of Figure 2), capacitor 27 discharges through resistor 26, and, since the high voltage supply (B-|-) is removed from anode 18 of thyratron vacuum tube 11 by the activation of relay 22, the thyratron ceases to conduct. Relay 22 subsequently de-energizes and relay arm 25 returns to relay contact 30, thus applying high voltage (B-|-) to anode 18 of thyratron vacuum tube 11, at which time a second cycle is commenced. It is apparent from Figure 2 that the time interval between the pulses of curves 204 and 205' is equal to the time interval x plus time interval y, or in other words, the time interval during which relay 22 remains energized plus the time interval (after B+ is applied to thyratron 11) required to charge capacitor 27 to a point at which ik falls sufiiciently and the bias on thyratron 11 is reduced to the firing point. From a practical standpoint, it is desirable that resistor 26 remain of constant magnitude. Hence, by the employment of potentiometer 12 and its selective adjustment, the pulse repetition frequency of the oscillator will be determined.

The output signal of the low frequency oscillator shown in Figure 1 will be one of sharp pulses. Such a circuit readily lends itself to the function of a triggering device to trigger, for example, a blocking oscillator or multivibrator. Relay 22 of the circuit of Figure 1 suggests additional uses for such an oscillator circuit. This is demonstrated in the circuit shown and described in Figure 3.

The circuit of Figure 3 is identical with that shown in Figure 1 with the exception that relay 22 has an additional relay arm 300 and contacts 301 and 302. When relay 22 is energized, relay arm 300 will engage relay contact 301 and short out capacitor 303, a circuit element of an associated circuit. The time interval during which capacitor 303 is shorted will depend, of course, upon the characteristics of relay 22 and the value of capacitor 23. However, the interval of time during which capacitor 303 of the associated circuitry is not shorted will depend upon the adjustment of tap 14 of potentiometer 12. Of course, additional relay arms may be employed to switch in or out, as desired, circuit elements of additional circuits. This switching action of the oscillator circuit, by virtue of the operation of relay 22 and its associated arms and contacts, suggests application to many radar systems to accomplish automatic strobing or range sweeping. Heretofore strobing has required the employment of an electric motor, associated cams, and other mechanical devices. It appears that the circuit shown and described in Figure 3 will reduce materially the cost of producing such strobing action for radar systems.

While particular embodiments of the present invention have been shown and described, it will be obvious to those skilled in the art that changes and modifications may be made Without departing from this invention in its broader aspects, and, therefore, the aim in the appended claims is to cover all such changes and modifications as fall Within the true spirit and scope of this invention.

I claim:

1. A device exhibiting a cyclical phenomenon the repetition frequency of which is in the order of one cycle per second or less including, in combination, a single gaseous discharge device having cathode, anode, and control electrodes, a resistance-capacitance circuit coupled to said cathode electrode of said gaseousdischarge device, said resistance-capacitance circuit having a relatively long time constant, means for deriving a voltage from said resistancecapacitance circuit for application to said control electrode of said gaseous discharge device, a relay coupled to said anode of said gaseous discharge device, said relay having a solenoid and a plurality of arms and contacts associated therewith, a capacitor shunting the solenoid portion of said relay, a first contact arm of said relay being coupled to said solenoid portion of said relay and also to said resistance-capacitance circuit, a first fixed contact of said relay being positioned to engage said first contact arm when said relay is in its de-energized condition, said fixed contact being maintained at a positive voltage, and a second fixed contact positioned to engage said first contact arm when said relay is in its energized condition, said second fixed contact being coupled to a portion of said resistance-capacitance circuit to discharge the capacitor therein.

2. A device exhibiting a cyclical phenomenon the repetition frequency of which is in the order of one cycle per second or .less including, in combination, a single gaseous discharge device having cathode, anode, and control electrodes, a resistance-capacitance circuit coupled to said cathode electrode of said gaseous discharge device, said resistance-capacitance circuit having a relatively long time constant, adjustable means for deriving a voltage from said resistance-capacitance circuit for application to said control electrode of said gaseous discharge device, a relay coupled to said anode of said gaseous discharge device, said relay having a solenoid and a plurality of arms and contacts associated therewith, a capacitor shunting the solenoid portion of said relay, a first contact arm of said relay being coupled to said solenoid portion of said relay and also to said resistance-capacitance circuit, a first fixed contact of said relay beingpositioned to engage said first contact arm when said relay is in its de-energized condition, said fixed contact being maintained at a positive voltage, and a second fixed contact positioned to engage said first contact arm when said relay is in its energized condition, said second fixed contact being coupled to a portion of said resistance-capacitance circuit to discharge the capacitor therein.

3. A low frequency triggering circuit including, in combination, a single gaseous discharge device having cathode, anode and control electrodes, at resistance-capacitance circuit coupled to said cathode electrode of said gaseous discharge device, said resistance-capacitance circuit having a relatively long time constant, adjustable means for deriving a voltage from said resistance-capacitance circuit for application to said control electrode of said gaseous I discharge device, a load impedance, a relay coupled through said load impedance to said anode of said gaseous discharge device, said relay having a solenoid and a plurality of contact arms and cooperating fixed contacts, a capacitor shunting the solenoid portion of said relay, a first contact arm of said relay being coupled to said solenoid portion of said relay and also to said resistancecapacitance circuit, a first of said fixed contacts being positioned to engage said first contact arm when said relay is in its de-energized condition, said fixed contact being maintained at a positive voltage, and a second fixed contact positioned to engage said first contact arm when said relay is in its energized condition, said second fixed contact being coupled to a portion of said resistancecapacitance circuit to discharge the capacitor therein.

4. A low frequency switching device including, in combination, a single gaseous discharge device having cathode, anode, and control electrodes, a resistance-capacitance circuit coupled to said cathode electrode of said gaseous discharge device, said resistance-capacitance circuit having a relatively long time constant, adjustable means for deriving a voltage from said resistance-capacitance circuit for application to said control electrode of said gaseous discharge device, a relay coupled to said anode of said gaseous discharge device, said relay having a solenoid portion and a plurality of contact arms and cooperating fixed contacts, a capacitor shunting said solenoid portion of said relay, a first contact arm of said relay coupled to said inductance portion of said relay and also to said resistance-capacitance circuit, a first of said fixed contacts being positioned to engage said first arm when said relay is in its de-energized condition said contact being maintained at a positive voltage, a second fixed contact positioned to engage said first contact arm when said relay is in its energized condition said second fixed contact being coupled across a portion of said resistance-capacitance circuit to discharge the capacitor therein, an auxiliary circuit component having a plurality of end terminals, a second contact arm and a plurality of fixed contacts for engagement therewith, said end terminals being connected to said fixed contacts and said contact arm for interconnelction of said end terminals during energization of said re ay.

References Cited in the file of this patent UNITED STATES PATENTS 

